Removal of Chromium (VI) from Tannery Effluent Using Bio-Char of <i>Phoenix reclinata</i>Seeds

The potential of the Senegal date palm (Phoenix reclinata) seed bio-char to remove chromium (VI) ions from aqueous solutions by adsorption was investigated. Adsorption experiments were performed on the tannery effluent and standard aqueous solutions of chromium (VI) for varying adsorbent doses, contact times, pH, temperatures, and interfering anionic ions by batch mode. Phoenix reclinata seeds (PRS) bio-char was used in the investigation and the residual chromium (VI) was determined using the atomic absorption spectrophotometer (AAS). Results showed that the bio-char removed up to 86% of chromium (VI) ions in the effluent at pH 2. The highest percentage adsorption registered was 97% in an aqueous solution of chromium (VI) at pH 1 and this dropped to less than 10% at pH greater than 2. A general increase in adsorption with the increase in temperature was observed but reduced when the temperature was raised beyond 60°C. The presence of interfering anions caused a reduction in the adsorption of chromium (VI) ions. The adsorption process fitted both Langmuir and Freundlich adsorption models and the maximum adsorption capacity, Qo, was 0.6593 mg/g. Thus, PRS bio-char can therefore be used by industries and institutions like secondary schools to treat effluents that contain chromium (VI).

Removal of Cr (VI) from Tannery Effluent and Aqueous Solution by Sequential Treatment with Microfungi and Basidiomycete-Degraded Sawdust

Removal of Cr (VI) from aqueous solution and tannery effluent in sequence with Cr (VI) resistant microfungi (Aspergillus niger, Penicillium chrysogenum) and sawdust degraded by basidiomycete (Gloeophyllum sepiarium) was investigated in the laboratory. Initial or primary treatment with microfungi reduced 200 mg/l Cr (VI) in aqueous solution by 64.6% - 78.2% while a markedly lower 0.52 mg/l Cr (VI) in tannery effluent was reduced by 72.4% - 84.6%. However, the residual Cr (VI) in both aqueous solution and tannery effluent was reduced to a non-detectable level after secondary treatment by passage through basidiomycete-degraded sawdust column. The recovery of 65.4% - 87.7% of the Cr (VI) removed by treatment microfungi by elution indicated adsorption as the major mechanism for Cr (VI) removal. The microfungi reduced BOD in tannery effluent by 85.3 ± 5.6 - 92.7 ± 6.8 and concomitantly removed Cr (VI), hence it is hypothesized that non-Cr (VI) constituents of tannery effluent may have interfered with biosorption of Cr (VI) by treatment microfungi. It is concluded that the two-stage sequential treatment process may be of potential cost-saving stratagem for removal of chromium from industrial wastes.

Adsorption of Chromium (VI) Using Nano-ZnO Doped Scrap Tire-Derived Activated Carbon

Nowadays, nano mineral modified biochars show a promising adsorption capacity for pollutants removals by combining the advantages of porous structure of biochar and unique property of nano minerals. In this work, nano-zinc oxide doped scrap tire derived activated carbon (nZnO-STAC) was synthesized by wetness impregnation method. Equilibrium data were analyzed using Langmuir and Freundlich isotherm models while the kinetics of the process were examined using Lagergren Pseudo-first and second order, intraparticle diffusion and Elovich kinetic models. Characterization of the activated carbon by Powder X-ray Diffraction (PXRD). The surface groups present on the activated carbon surface were determined using the Fourier Transform Infra-Red Spectroscopy (FTIR) analysis. Optimization studies were carried out to determine the effects of pH, initial metal concentration, adsorbent dosage, contact time and adsorbent particle size on the Cr (VI) removal efficiency. The results showed optimum Cr (VI) removal at pH 3, 10 mg/L concentration, 120 minutes of contact using 1000 - 1400 μm adsorbent particle size at a dosage of 2.5 g/L. The adsorbent structure was found to be predominantly amorphous. The chromium removal efficiency of the adsorbent was around 81.6%. Of the tested kinetic models, the pseudo-second order model exhibited the best fit with the experimental data with an R2 value of 0.9744. This study clearly demonstrates the feasibility of using the nano-ZnO doped scrap tyre derived activated carbon adsorbent for the remediation of chromium (VI) polluted industrial wastewaters.